Heat pack



FIG. 1 is a front perspective view of a heat pack showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is an end view thereof, the opposite end view being a mirror image of the view of FIG. 3; and,

FIG. 4 is a top plan view thereof, the bottom plan view being a mirror image of the view of FIG. 4. 

The ornamental design for a heat pack, as shown and described. 